This invention relates to automatic sensing of liquid level in a sample container, and more particularly to a novel adapter for holding a sample container to facilitate liquid level sensing, and a novel method of sensing liquid level in a sample container.
Ultrasonic liquid level sensing is often used in automatic sample analysis systems of the type disclosed in U.S. Pat. Nos. 5,268,167 and 5,399,497. During automated sample analysis a liquid sample, such as blood serum, is subjected to a variety of tests. The serum sample, which is used as a source material for the tests, is usually placed in a relatively small container of fixed diameter, such as a Microtainer(copyright) tube, since the desired tests can be performed with relatively small amounts of diluted sample. For each discrete test on the serum a selected amount of diluted sample is aspirated from the sample container and combined with a predetermined amount of reagent to produce a chemical reaction that corresponds to a distinctive test on the sample.
The sample tests provide chemical information relating to different characteristics of the blood to assist in determining the health or well being of the individual being tested.
The quantity of sample which is used in each reagent test must be precisely controlled because test interpretation is based on an expectation that a predetermined amount of sample is combined with a predetermined amount of reagent. One known way of ensuring that the reagent tests are based on selected amounts of sample and reagent is to measure the sample level in a sample container before and after each aspiration of sample and to perform corresponding measurements on the reagent in a reagent container.
The liquid level measurement information will confirm that the intended amount of sample has in fact been used in a specific test. Thus consecutive measurements of sample level in a sample container provide confirmation that the required amount of liquid is removed from the sample container for each test. The sample level measurements for each test also provide an ongoing determination of the amount of liquid that remains in the sample container.
In known sample analysis systems of the type previously referred to it is common practice to transport one or more sample containers to different locations in the sample analysis system. Sample containers are usually transported in sample tube racks that carry larger diameter tubes than the Microtainer(copyright) tube, such as Vacutainer(copyright) tubes which have other uses in the sample analysis system. The sample tube rack preferably maintains tubes of all sizes in an upright position since the tubes are often in an open condition.
In order to simultaneously transport relatively small sample containers, such as Microtainer(copyright) tubes with other larger diameter tubes, each Microtainer(copyright) tube is usually supported in a larger diameter tube. However, because of a great disparity in size between the Microtainer(copyright) tube and the Vacutainer(copyright) tube it is necessary to cradle the Microtainer(copyright) tube in an intermediate holding device such as an Easi-nest(copyright) holder.
The Easi-nest(copyright) holder, which is open at one end and closed at the opposite end, has a tapered inside surface that is sized to bear against the Microtainer(copyright) tube when the Microtainer(copyright) tube is pushed into the Easi-nest(copyright) holder. The Easi-nest(copyright) holder also has a flange at the mouth portion that is large enough to rest on the mouth portion of the Vacutainer(copyright) tube. The support of a Microtainer(copyright) tube in an Easi-nest(copyright) holder held in a Vacutainer(copyright) tube is referred to herein as a sample tube support system or a Microtainer(copyright) tube support system.
The sensing of liquid level in the Microtainer(copyright) tube can be accomplished while the Microtainer(copyright) tube is supported in an Easi-nest(copyright) holder and elevated in a Vacutainer(copyright) tube held in a test tube rack or sample tube rack.
One known method of sensing liquid level is to employ an ultrasound detector. The ultrasound detector is located at a predetermined elevation over the travel path of the sample tube rack that holds the Microtainer(copyright) tube support system.
During liquid level sensing the ultrasound detector emits an ultrasonic wave directed against a horizontal surface of the Microtainer(copyright) tube support system that is proximate the liquid level. The ultrasonic wave is reflected as a sound echo from the horizontal surface back to the ultrasound detector. The characteristics of the echo are interpreted in a known manner by the ultrasound detector to indicate the distance between the ultrasound detector and the surface that reflected or produced the echo.
If the echo producing surface is in fact the liquid level in the Microtainer(copyright) tube than the distance between the liquid surface and the ultrasound detector can be determined by measuring the duration of time between the emission of the ultrasound wave and the receipt of the echo from the liquid level.
However, when a sample rack includes a Microtainer(copyright) tube supported in an Easi-nest(copyright) holder and a Vacutainer(copyright) tube it is difficult to selectively direct an ultrasonic wave against only the liquid level in the Microtainer(copyright) tube. To deal with this problem an ultrasonic wave is periodically emitted as the sample rack passes under the ultrasound detector. Ultrasonic waves are thus sequentially directed against other horizontal surfaces of the Microtainer(copyright) tube support system in addition to the liquid level. These horizontal surfaces include the mouth portion of the Microtainer(copyright) tube and the mouth portion of the Easi-nest(copyright) holder.
Based on a known height of the mouth portion of the Microtainer(copyright) tube from a reference level we can determine a first distance between the ultrasound detector and the mouth portion of the Microtainer(copyright) tube. Also based on a known height of the mouth portion of the Easi-nest(copyright) holder from the reference level we can determine a second distance between the ultrasound detector and the mouth portion of the Easi-nest(copyright) holder. Thus the mouth portion surfaces of the Microtainer(copyright) tube and the Easi-nest(copyright) holder can be identified from their corresponding echoes. The remaining echo would thus be associated with the liquid level in the Microtainer(copyright) tube.
Generally the liquid level 110 in a Microtainer(copyright) tube 20 is initially at a higher level than the mouth portion 140 of the Easi-nest(copyright) holder 132 (see FIGS. 10 and 11). However, as liquid 80 is depleted from the Microtainer(copyright) tube 20 the liquid level 110 recedes toward the mouth level 140 of the Easi-nest(copyright) holder 132. When liquid level 110 in the Microtainer(copyright) tube 20 closely approaches the level of the mouth portion 140 of the Easi-nest(copyright) holder 132 it becomes difficult to distinguish between the echo from the liquid level 110 in the Microtainer(copyright) tube 20 and the echo from the mouth portion 140 of the Easi-nest(copyright) holder 132. Thus there is a range of liquid level 110 in the Microtainer(copyright) tube 20 that can be confused with the level of the mouth portion 140 of the Easi-nest(copyright) holder 132 which can lead to errors in liquid level sensing.
It is thus desirable to provide a sample tube support structure for a sample container such as a Microtainer(copyright) tube that facilitates distinguishing a liquid level surface echo from an echo produced by a structural surface of the Microtainer(copyright) tube support system.
Another problem in measuring liquid level in a Microtainer(copyright) tube supported in an Easi-nest(copyright) holder is that the amount by which a Microtainer(copyright) tube projects from an Easi-nest(copyright) holder may vary due to manufacturing tolerances. Inconsistent positioning of the Microtainer(copyright) tube in the Easi-nest(copyright) holder is also common because the Microtainer(copyright) tube is usually manually pushed into snug engagement with the tapered surface of the Easi-nest(copyright) holder and there is no fixed stop position for the Microtainer(copyright) tube in the Easi-nest(copyright) holder. It is thus desirable to provide a Microtainer(copyright) tube support system wherein the Microtainer(copyright) tube is always located in the same position in the support system.
Among the several objects of the invention may be noted the provision of a novel support system or adapter for holding a sample tube container or Microtainer(copyright) tube in a sample rack to facilitate liquid level sensing in the sample container, a novel adapter for holding a sample container to facilitate liquid level sensing in the sample container by an ultrasound detector, a novel adapter having a reduced diameter mouth portion to provide direct support for a sample container, a novel adapter for direct support of a sample container without an intermediate support device between the sample container and the adapter, a novel adapter that directly supports a sample container at a lip flange of the sample container, a novel adapter having a body structure that diverts ultrasound wave echoes away from the ultrasound detector, a novel adapter having a body portion with a tapered section to divert ultrasonic wave echoes away from the ultrasound detector, a novel adapter that holds a sample container and is substantially invisible to an ultrasound detector to enable the ultrasound detector to receive only the sound echoes from the lip flange of the sample container and from the liquid level in the sample container and not receive echoes from any other structure of the sample tube support system, and a novel method of ultrasonically sensing liquid level in a sample container.
Other objects and features of the invention will be in part apparent and in part pointed out hereinafter.
In accordance with the invention an adapter for holding a sample container is a generally tubular structure having a main body portion and a tapered body portion. The main body portion preferably has a fixed diameter. The tapered body portion extends from the main body portion to a mouth opening that is of lesser diameter than the main body portion. The tapered body portion has an outer diameter that increases in magnitude in a direction from the mouth opening toward the main body portion.
The mouth opening of the adapter is sized to receive a relatively small diameter sample container such that a lip portion or lip flange of the sample container rests upon the mouth opening of the adapter. The tapered body portion of the adapter includes inner surface projections that bear slightly against the sample container when it is received in the mouth opening of the adapter.
In some embodiments of the invention the adapter is formed as a two piece stricture with one component being the tapered body portion and the other component being the main body portion.
In another embodiment of the invention the adapter has an enlarged bottom opening. The adapter can thus be formed as a one piece integral structure.
In one embodiment of the invention the main body portion and the tapered body portion are joined together at a snap fit joint. The snap fit joint includes a first lip that projects radially outwardly of the one of the main body portion and the tapered body portion and a second lip that projects radially inwardly of the other of the main body portion and the tapered body portion. Thus the main body portion and the tapered body portion can bypass each other with slight interference to permit one the lips to bypass the other lip to form an inseparable snap fit joint between the main body portion and the tapered body portion.
In a further embodiment of the invention the main body portion and the tapered body portion are joined together at complementary shaped step portions formed at the joint.
In some embodiments of the invention the bottom portion of the adapter has a curved semi-spherical shape.
In several embodiments of the invention the tapered body portion of the adapter has two distinct tapered sections. One of the two tapered sections has a lesser amount of slope than the other tapered section. Preferably the tapered section with the lesser amount of slope includes the mouth opening of the adapter.
When a sample container is provided with serum and placed in the adapter the entire body portion of the sample container is received in the adapter. Thus only the lip flange of the sample container rests upon the mouth opening of the adapter.
The main body portion of the adapter can be of the same diameter as that of a standard size test tube and placed in a sample tube rack with other test tubes of standard diameter. The rack can be transported below an ultrasound detector for purposes of liquid level sensing. The ultrasound detector emits sound waves that are reflected back to the detector as echoes from only the mouth portion of the sample container and the liquid level within the sample container.
Any ultrasonic waves that reach the tapered body portion of the adapter are reflected away from the sound detector. Therefore, the sound detector does not receive any echoes from the adapter and consequently does not recognize any surfaces of the adapter. The adapter is thus essentially invisible to the ultrasound detector.
Since the lip flange of the sample container is always at the same position in the adapter the sound detector can always recognize the lip flange of the sample container based on the echo it produces. The only other echo received by the sound detector is from the liquid level surface which is always below the lip flange of the sample container. Therefore the sound detector can clearly distinguish between the echo from the liquid level surface and the echo from the lip flange of the sample container. The sound detector can also clearly distinguish any echoes from the sample rack, which are substantially weaker than the echoes from the sample container and the liquid level.
Since no other echoes from the adapter or the sample container are received by the sound detector the adapter provides a reliable means for facilitating the sensing of liquid level in the sample container.
The invention accordingly comprises the constructions and methods hereinafter described, the scope of the invention being indicated in the claims.